There is an ongoing effort to generate and process signals of higher frequencies, larger bandwidths and greater amplitudes. Accordingly, there is an ongoing effort to construct electronics, and more particularly, integrated circuits capable of generating and processing such high-frequency, high-power signals without adverse effects. Recently, there has been growing interest in using silicon-based integrated circuits at high microwave and millimeter wave frequencies. The high level of integration offered by silicon enables numerous new topologies and architectures for low-cost and reliable system on chip (SoC) applications at microwave and millimeter wave bands, such as broadband wireless access, vehicular radars, short range communications, ultra narrow pulse generation for ultra-wideband (UWB) radar and extremely wideband (EWB) applications.
However, the persistent barrier to such advances in technology lies within the elemental components with which integrated circuits are built. Power generation and amplification is one of the major challenges of processing signals at millimeter wave frequencies. This is particularly critical in silicon integrated circuits due to the limited transistor gain, efficiency, and breakdown on the active side and lower quality factor of the passive components due to ohmic and substrate losses. Moreover, the operational limitations of passive and/or active devices, for example transistors, limit the capabilities of a circuit or device to process signals beyond a maximum frequency fmax. In fact, as the maximum operational frequency fmax of a particular transistor is a theoretical rating, in practical applications, the transistor would hardly be useful at fmax to perform any kind of meaningful operation. Be it analog amplification or digital switching, circuits using the transistor can only operate with bandwidths and frequencies that are only a small fraction of such theoretical limits.
One of the solutions for overcoming the drawbacks associated with power amplification is power combining. Power combining is particularly useful in silicon where a large number of smaller power sources and/or amplifiers can generate large output power levels reliably. This would be most beneficial if the power combining function is merged with impedance transformation that will allow individual transistors to drive more current at lower voltage swings to avoid breakdown issues. However, most of the traditional power combining methods use either resonant circuits, and thus, are narrowband or employ broadband resistive networks that are inefficient.
More recent developments have turned to common electromagnetics, and more particularly, to principles of wave propagation. The concept of a solitary wave was first introduced to science by John Scott Russell when he observed a wave which was formed when a rapidly drawn boat came to a sudden stop in narrow channel. According to his diary, the wave continued “at great velocity, assuming the form of a large solitary elevation, a well-defined heap of water that continued its course along the channel apparently without change of form or diminution of speed.” These solitary waves, or solitons, have become important subjects of research in diverse fields of physics and engineering. The ability of solitons to propagate with small dispersion can be used as an effective means to transmit data, modulated as short pulses over long distances.
In light of the foregoing, there is a need for improved circuit topologies capable of more reliably and more effectively processing high-frequency and high-power signals from low-frequency and low-power input. Moreover, there is a need for novel circuit architectures which employ commonly used structures in electromagnetics and the mathematical theory of linear and nonlinear wave propagation to overcome the performance limitations of passive and active devices.